The present invention relates to an elevator installation with braking equipment and to a method for braking and arresting an elevator installation.
An elevator installation comprises an elevator car which moves in a vertical direction within guide tracks or guide rails. The elevator car is in the case of need braked or held at standstill by braking equipment. For holding or braking the elevator car a braking force is required. The braking equipment for that purpose usually utilizes at least two brake units which when required press at least one brake lining against a counter-surface. This pressing is effected by means of a normal force. The braking force of a brake lining is determined by the normal force together with the coefficient of friction defined by the brake lining, the counter-surface and any intermediate layers. The counter-force is usually defined by a surface of the guide track or the guide rail.
German patent DE 3934492 shows braking equipment for an elevator car which in the case of braking engages the guide rail, wherein the braking force is regulated by means of an acceleration sensor. The braking force in that case is applied by a spring, wherein in the case of a too-high deceleration value the braking force can be reduced or, in the case of too-low deceleration, amplified by a regulatable magnet.
A disadvantage of this equipment is that the brake equipment is not designed for holding an elevator car in a stopped position, such as, for example, at a regular stop at a floor. In addition, the braking equipment is set to a fixed value which is predetermined by the spring and which in the working case is either moved towards as quickly as possible, which leads to a significant transient process, or which in the working case is moved towards slowly, controlled by the counter-force of the stroke magnets, whereby the speed in the case of a fully laden car disadvantageously increases. Moreover, the regulatable magnet is expensive and heavy, it additionally absorbs a large amount of power, and monitoring of the operational readiness of the equipment can be difficult to carry out. The power requirement is high because the maximum possible braking force to be applied by the braking equipment is oriented towards a freely falling, fully laden car. However, as a rule, for example in the case of braking from excess speed, a car which is unladen or laden only to a small extent is braked. In this connection, only small braking forces are required.
Example: A typical stroke magnet produces, in the case of a power requirement (PM) of up to 4000 W, a stroke force/thrust force (FM) of approximately 1500 N. With the assumption of a lever translation (i) of 3 and a coefficient of friction (μ) of 0.2 there results according to equationFBR=FM×1×μ×2a braking force regulating range (FBR) of +/−1800 N per brake housing, or in the case of two brake housings a regulating range (FBR2) of +/−3600 N results. The weight of a corresponding stroke/thrust magnet amounts to up to 50 kg or for two magnets up to 100 kg. With consideration of an additional spring per brake housing, which produces a braking force in each instance of 5000 N, a total braking force of 10,000 N with a braking force regulating range of +/−3600 N thus results in the case of two brake housings. A braking installation with low braking forces of that kind is merely sufficient for safety braking of a car with a total weight of about 1000 kg (useful load 480 kg and car mass 520 kg). The weight of this elevator car is in that case increased by approximately 10% and the necessary electrical regulating power is up to 2×4 kW.
U.S. Pat. No. 5,323,878 discloses further braking equipment with two brake units. The brake units are arranged in the region of a drive motor. The braking forces are transmitted by way of support elements from the drive motor to the car. The braking force of each brake unit is determined by a brake control unit with consideration of the car speed or car load. In the mentioned example, the braking force is produced by means of a spring, wherein a hydraulic piston force counteracts this spring. This embodiment corresponds with a currently usual, safer mode of construction, since in the case of failure of the hydraulic system the springs brake with their maximum possible force. The requisite hydraulic piston force of each brake is calculated by a brake control unit with consideration of the car speed or car load and hydraulically controlled. The hydraulic piston force must in that case be established with consideration of brake-specific characteristics, such as piston diameter, spring force or installation geometry of each brake unit.
A disadvantage of this equipment is that relevant influencing factors, which influence the braking force, are not recognized and not taken into consideration. A defect of a spring, wear of a brake lining or jamming of brake levers can lead to a relevant influencing of the braking force, which is not recognized. Moreover, the brake control unit must take into consideration brake-specific characteristics, such as piston diameter, spring force or installation geometry, of each brake unit, since the brake control unit presets the hydraulic piston force for each individual brake unit. These disadvantages potentially increase the susceptibility to fault in the case of installation and in the case of replacement as well as in operation; hence the brake-specific characteristics of each brake unit have to be input at the brake control unit.